Update Dockerfile to use working python/debian img
Update Dockerfile to use working python/debian img

To ensure docker builds continue to work, needed to update base image to
python:2.7.16-strech, to continue using openjdk-8-jre. I tried switching
to openjdk-11-jre, but it doesn't work with the (old!) version of
Solrmarc we're using.

unt-libraries/catalog-api,unt-libraries/catalog-api,unt-libraries/catalog-api,unt-libraries/catalog-api